Saprolegnia Water Fungus

Ponds are an ecosystem, and as such, contain plants, algae, invertebrates, protozoa, bacteria and molds or fungi. These life forms in our ponds are all dependent upon each other. Known as symbiosis (the relation between two different species of organisms that are interdependent; each gains benefits from the other). An extreme form of this are parasites, where one life form lives at the expense of another. Saprolegnia or water fungus is one of the more common forms of this.

Saprolegnia will only attack a weakened fish that has already been infected by another disease or parasite. Fungus will not attack a strong and healthy fish, so therefore the best way of avoiding an attack is to keep your pond as clean as possible and your fish healthy and fed well.

Although it may take a while to happen, Fungus will eventually spread through the fish and kill it.

Saprolegnia lives in fresh water environments and needs water to grow and reproduce. It can also be found in brackish water and moist soil. It flourishes in colder water, but also lives well in a wide range of water temperatures extending from 37 deg F to 91 deg F (3 to 31 deg C).

Seen under a microscope, the fungus is seen to be composed of filaments with spherical ends. It is these that house the zoospores, or the “seeds” of Saprolegnia, which allow it to increase and spread. It is these filaments that give the fungud it's 'cotton-like' appearance, they are called hyphae.
It is the hyphae, or to be precise, the hooked, foot-end of the hyphae, which penetrate the tissue of the fish as they look for nutrients.

When seen in the water Saprolegnia looks like fluffy cotton, but when a fish is removed for examination it presents as a matted mess of slime. Saprolegnia starts out either white or grey in color.  Over a short period of time, it may turn brown or green as organic particles in the water (such as algae) stick to the filaments.

Saprolegnia can be easily confused with epistylus, a freshwater parasite that also looks like a white cottony substance growing on the skin of the fish. However, Epistylus does not gather organic particles and will remain white. Confirmation of whether Saprolegnia or  Epistylus is present should be done with a microscope.
The fungus' favourite food is dead organic tissue. We can usually see evidence of Saprolegnia on dead and dying fish, live and dead fish eggs and even food left in the water so long that it has begun to rot.
Be aware around spawning time and clear infertile eggs from the pond as soon as possible as typically we see infertile koi eggs being infected first. The fungus then spreads to kill live, fertile eggs. Infected eggs have the typical fluffy cotton wool-like covering. It also likes to feast on exposed and decaying tissue caused by bacterial infections, such as ulcers. It is most prevalent on the head and fins of the fish as these are the areas that offer the least amount of natural resistance provided by the mucous coat.
 
Symptoms

grey or white growth on fins and skin
white areas grow larger and more cotton like as the disease progresses


Primary or Secondary Invader

Usually Saprolegnia is thought of as a “secondary” invader. This means that something else ie Anchor Worm has broken through the barrier of the fish’s skin and allowed bacteria to enter. This provides direct tissue access for the fungus' hyphae to embed themselves.
When treating a case of Saprolegnia it is vitally important to treat BOTH the fungus and the underlying primary cause.

However, Saprolegnia can also be a primary invader under the right conditions. Cold water and dramatic fluctuations in temperature can cause great stress to fish, causing suppression of their immune system. As previously stated Saprolegnia flourishes in cold water and produces and releases increased zoospores into the water. The combination of these coupled with weakened immune systems means that Saprolegnia can cause major problems in colder water. Saprolegnia commonly causes deaths over the winter.


The following conditions support the spread of Saprolegnia:

open wounds that provide access to tissue
Parasites and pathogens – the parasites cause wounds that allow pathogens (like bacteria) to enter the tissue this gives the fungus a chance to take hold thus causing stress to the fish
overcrowding – stress and too many organics in too little water
pollution – stress and reduced water quality
handling – stress and removal of the mucous coat on the fish
spawning – stress and physical damage
water quality – stress and reduced physiological conditions
water temperature changes – stress.   

   
The recurring message from the above is that stressed fish are far more susceptible to disease and parasites. First and foremost you need to maintain as healthy and stress free environment as possible.

In healthy conditions,  fish have some natural protection against Saprolegnia with the mucus layer being the most effective first line of defense. This layer provides the ability to reject an  attack by sloughing off a layer of mucous and sending the Saprolegnia with it. The mucus layer also provides a natural fungicide at the cell-level. Therefore you can see that incorrect handling or any activity that reduces the mucus coat offers an increased opportunity for the fungus to take hold.

If you are unlucky enough to have a fish with the infection, once it has taken hold, Saprolegnia can spread rapidly over the surface of the fish. While it does not penetrate deeply into tissue layers like an ulcer, for example, damage can still be deadly. This is particularly the case if the gills are affected. The more widely spread the fungus becomes there is obviously less chance of recovery. Early intervention is imperative.


Treatment

Fish fungal infections are difficult to treat and mould cannot ever be eliminated from any fish keeping systems. Therefore any treatment plan must take account of any factors that may have contributed to the development of the infection and these should be resolved and/or treated at the same time.

Topical treatments:

Use strong malachite green solution (100mg/ litre) to clean the lesion and apply a water-proof cream.
   
Long-term bath treatments:

Salt: 1–5g / litre indefinitely
Malachite green: 0.10mg/litre – three treatments at three-day intervals


As with any treatment, be aware of the type of fish you have and the treatments suitability for use with those fish.

Malachite Green can be used with Sturgeon present, do not use the Malachite Green and Formalin mix.